In recent years, a universal serial bus (USB) connectable battery-powered electronic apparatus such as a digital camera has generally dealt with being charged or fed with electric power by USB standard bus power (hereinafter, referred to as USB bus power). For example, some USB connected digital cameras can switch an operation mode including a charging mode, a playing mode, and a shooting mode during USB connection. This operation mode switching is accomplished by switching between plural pieces of USB device class information (configuration information) that the apparatus has.
There are difficulties as follows concerning these functions in an electronic apparatus including a chip which is relatively high in power consumption and includes a USB connecting function like a large-scale core chip which is formed into one chip including a USB device function.
A first difficulty is that the electronic apparatus may not be started up with only the USB bus power in a case where an electronic apparatus has no remaining battery charge. This is caused by the fact that power of 5V×500 mA at a maximum can be obtained with the USB bus power after configuration, but the power is limited to 5V×100 mA under the USB standard before the configuration, and thus, the configuration may not be executed unless the electronic apparatus is started up. That is, a large amount of power (large amount of current) may not be obtained with the USB bus power at the time of starting-up before the configuration and the electronic apparatus may not be started up owing to power shortage in the case of no remaining battery charge.
A second difficulty is that when USB device class switching is performed in a state where the electronic apparatus is operating, the class switching may not be performed owing to the power shortage in the case of no remaining battery charge of the electronic apparatus. This is caused by that because a USB is electrically disconnected and reconnected at the time of class switching, a configuration state is released into an initial state and a limitation on the power supplied by the USB bus power is lowered to 5V×100 mA or less.
The configuration is also referred to as enumeration, which is an initial process executed between a USB connected host apparatus (for example, personal computer) and a device apparatus (for example, digital camera). The process on the configuration is executed to establish a device class to be applied and to request power from the device apparatus to the host apparatus. Examples of the device class include a mass storage class used for USB memory and a human interface devices class used for USB mouse.
There is proposed a technology in which two USB connectors on the host side are used regarding a USB connected electronic apparatus to resolve shortage of the power supplied by the USB bus power (see Patent Document 1, for example). The above technology discloses a structure in which currents output respectively from the USB connectors on the host side are collectively supplied to the electronic apparatus such that power of 5V×1 A at a maximum can be supplied by the USB bus power after the configuration.                [Patent Document 1] Japanese Laid-open Patent Publication No. 2012-8716        